A NAND type flash memory device having a 3D structure is known as one of semiconductor devices. When the NAND type flash memory device having the 3D structure is manufactured, there is executed a step of forming a deep hole in a multilayer film, in which two layers having different dielectric constants are alternately and repeatedly laminated, by etching the multilayer film. Such an etching technique is disclosed in, e.g., U.S. Patent Application Publication No. 2013/0059450.
Specifically, there is disclosed in U.S. Patent Application Publication No. 2013/0059450 a technique for etching the multilayer film by performing a main etching process for exposing a target object having a mask made of amorphous silicon and formed atop the multilayer film to a plasma of a processing gas containing CH2F2 gas, N2 gas and NF3 gas and an overetching process for exposing the target object to a plasma of a processing gas containing CH2F2 gas, NF3 gas, CH3F gas and CH4 gas.
The above multilayer film needs to be etched at a high speed. Meanwhile, an etching stop layer may be formed beneath the multilayer film in order to protect wiring or the like provided below the multilayer film. Although it is preferred to etch the multilayer film having the etching stop layer in a high speed, the etching stop layer may be considerably removed in the case of etching the multilayer film by using, e.g., an etching gas that contributes to the high etching speed.